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  1. #1
    Doug Mossing's Avatar
    Doug Mossing Guest

    Default Oversized wiring

    Recently I inspected a home with dual split system AC units. One was rated for 40 amps and the other for 25 amps. The larger AC unit had a 40 amp double breaker (Square D) and the smaller a 20 amp double breaker in the electric service panel. However both units used the same gauge copper wiring (rated for the larger unit) from the unit to the eletric service panel. I wrote it up as using 'oversized wiring' for the smaller unit. The customer service rep for the builder stopped me a week later and said they had checked with their electrician who stated that naturally, 'you cannot use undersized wiring because it will overheat - but you can use oversized wiring'. This is in AZ. If someone would confirm this statement one way or the other I'd appreciate it.

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  2. #2
    Join Date
    Mar 2007
    Location
    Ormond Beach, Florida
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    25,309

    Default Re: Oversized wiring

    Quote Originally Posted by Doug Mossing View Post
    I wrote it up as using 'oversized wiring' for the smaller unit. The customer service rep for the builder stopped me a week later and said they had checked with their electrician who stated that naturally, 'you cannot use undersized wiring because it will overheat - but you can use oversized wiring'.
    Regardless of where you are,you cannot "oversize" wire something.

    Well, with one exception ... if the conductor is too large for the rated and allowed conductor sizes for a terminal, then oversize is bad, because you would need to cut some strands off, and that is a supper no-no.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  3. #3
    Join Date
    Mar 2007
    Location
    Healdsburg, CA
    Posts
    1,741

    Default Re: Oversized wiring

    Over fusing -yah
    Over size conductors - ynet.

    Jerry McCarthy
    Building Code/ Construction Consultant

  4. #4
    Richard Rushing's Avatar
    Richard Rushing Guest

    Default Re: Oversized wiring

    Doug look at it this way...

    If the breaker is oversized, this means one thing-- it can allow the conductor to overheat prior to tripping. The breaker is designed to trip at a certan temperature, which will not be met because it is oversized for the smaller conductor. Overheating-- not good!!

    If the conductor is oversized, the breaker will reach it's tripping pont (well it's designed to anyway) before the conductor fries (theoritically).

    As Jerry stated, the one thing you can't do is use an oversized conductor and trim back the strands just to make it fit the lug-- just bad business...


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